1. Field of Invention
The present invention relates to a viscometer which measures the viscosity of a fluid by rotating a bob within the fluid, the viscosity of which is to be determined. Measurement of the energy necessary to rotate the bob within the fluid is used to determine the viscosity of the fluid. This invention could be used in a conduit such as pipe or manifold to measure the fluid within the working environment of the fluid or it could be operated in a laboratory environment.
2. Description of Prior Art
The measurement of the viscosity of a fluid flowing in a pipe or other conduit is well known but can be problematic. Particularly difficult fluids to measure are fracturing fluids and gels used in fracturing of well formations. The viscosity of the fluid is, of course, measurable before it is pumped into the well, but this measurement is not always satisfactory because the viscosity of the fluid may change in the well. Heat and other well conditions may affect the fluid in ways that are not entirely predictable. Therefore, it is desirable to be able to measure the viscosity of such fluids “on the fly” as the fluid is flowing through the pipe. A viscometer for this purpose is called an “in-line” viscometer.
U.S. Pat. No. 4,524,611 teaches a rheometer comprising a hollow body 2 with an inner shaft 9 which is driven to rotate via a coupling with magnet 12A. Unfortunately, this rheometer could not be used in-line because the magnet 12A would become submerged in sample fluid, which would inevitably create measurement errors due to the fluid flow. Additionally, the position of inner shaft 9 is maintained at top and bottom by a pin and jewel bearing, which are not configured such that they could sustain as much radial directional disturbance as would be present in a pipeline filled with a flowing fluid.
U.S. Pat. No. 7,568,380 teaches a patent for an in-line turbine viscometer. It suspends a turbine within a pipe containing a flowing fluid, and uses magnets as the impetus for the rotation of the turbine. The drawback to this approach is that the flow of the fluid makes it impossible to control or even define a specific shear rate for the turbine rotation. If fluid flow falls below a certain level, measurement becomes riddled with errors or stops entirely.
U.S. Pat. No. 6,640,617 teaches an in-line apparatus and a method for determining the viscosity of a fluid which places an electrical rotary drive having a stator with a stator winding and a rotational body into a pipeline filled with a flowing fluid. The rotational body is suspended and driven to rotate by a magnetic field generated by sets of coils. This apparatus is very complicated and expensive to manufacture due to its sophisticated magnetic field suspension and control.
U.S. Pat. No. 4,643,021 teaches a method of measuring the rheological characteristics of a fluid by magnetically suspending a cylinder immersed in the fluid which is to be tested and rotating said cylinder via magnetic suspension. This apparatus is not, however, suitable for use as an in-line measurement method and further, is complicated and expensive to manufacture due to the nature of magnetic suspension technology.
It is an object of this invention to provide a practical and affordable in-line device for accurately testing the viscosity of a flowing fluid without compromising the integrity or performance of the working environment of the fluid.
It is another object of this invention to provide a viscosity measurement device which uses magnetic force to suspend a bob in the fluid, the viscosity of which is to be determined, and rotate the bob using magnetic coupling, measuring the energy required to rotate the bob and using that measurement to determine the viscosity of the fluid.
It is another object of this invention to provide a viscosity measurement device which requires substantially less maintenance work than other designs yet meets industry standards of accuracy, repeatability, durability, and ease of cleaning